1. Field of the Invention
The invention relates to equipment for applying a coating liquid to a moving strip of material, and in particular to a coating pan construction which holds a quantity of coating liquid which is applied directly to one side of the strip or is applied to a transfer roll mounted above the pan and partially submerged in the coating liquid in the pan. More particularly, the invention relates to a coating pan construction having a pair of spaced weirs mounted on the pan which forms a reservoir for a pool of coating liquid which accurately controls the wetted area of the transfer roll or the width of the area to which liquid is applied to the moving strip, and which provides a cleaner pool of coating liquid.
The invention also relates to an improved method of applying a coating liquid to one side of a moving strip of material, and in particular to a method of applying and accurately controlling the moving strip surface area that is coated.
2. Description of the Prior Art
Prior coating equipment and coating methods use pan constructions which hold a supply of coating liquid and in which the strip material backup rolls or the liquid transfer rolls are placed so that the roll journals pass over the pan ends with the body of the roll dipping a short distance into the coating liquid. The rolls dip into the coating liquid a short distance and pick up a quantity of the liquid for transfer to a web or strip of material moving or passing over and in contact with the top of the coating roll. A second roll may be mounted above and in contact with such lower rolls for receiving a supply of coating liquid from the pickup rolls for transfer to a moving strip of material. Likewise, the strip of material may pass directly through the coating liquid moving about and beneath the backup roll partially submerged therein.
It was necessary with such prior coating equipment and in such coating methods to use a coating liquid holding pan of size sufficient to accommodate strips of material of various widths. This resulted in requiring large quantities of coating liquid to completely fill the pan to the proper level even though the width of the strip material being coated was quite small in comparison to the length of the pan. Likewise, even in those situations where a pan roll is used as a backup roll the uncovered portion of the roll is submerged in the coating liquid, requiring frequent and expensive cleanups of the roll and pan.
These prior pans usually had a remote coating liquid supply reservoir to maintain the supply of coating liquid in the pans at the desired level by replacing the liquid that is deposited on the moving strip being coated. Impurities, however, continued to collect within the pan from the surrounding atmosphere and from the strip being coated.
The lighter impurities floating near the top of the coating liquid were transferred to the coated web or strip of material resulting in an uneven coated surface and rough or uncoated areas on the coated strip. The heavier impurities settle to the bottom of the pan, necessitating numerous equipment shutdowns for cleaning the pan, after draining off the coating liquid.
Air bubbles also form on the top of the coating liquid within the pan due to the slight agitation of the liquid by the rotating liquid transfer roll or material backup roll and by the runoff of the excess coating liquid. These bubbles also cause an uneven coating to be applied to the moving strip.
The coating liquid in prior coating equipment and methods works out beyond the roll ends due to the entire roll body being submersed in the coating liquid. This results in the roll ends being "wet" and a supply of coating liquid accumulates thereon. The accumulated coating liquid builds up on the roll journals and mounting mechanism requiring constant maintenance of the same. Likewise, the edges of the strip material being coated also are coated. This is not desirable in many applications since some of the coating material passes to the uncoated side of the strip material.
Thus, a need has existed for coating apparatus and for a method of applying coating liquid to strip material which enable the coating width on the strip or transfer roll to be adjustably and accurately controlled, and which reduce harmful impurities in the coating liquid which heretofore resulted in producing imperfect coatings on the moving strip being coated.